About 143 million pounds are targeted, but the amount may be much greater due to processing methods.

The U.S. Department of Agriculture announced the largest beef recall in its history Sunday, calling for the destruction of 143 million pounds of raw and frozen beef produced by a Chino slaughterhouse that has been accused of inhumane practices.

However, the USDA said the vast majority of the meat involved in the recall -- including 37 million pounds that went mostly to schools -- probably has been eaten already. Officials emphasized that danger to consumers was minimal.

The recall applies to beef slaughtered at the Hallmark/Westland Meat Packing Co. since Feb. 1, 2006. The company has produced no meat since Feb. 4 of this year, when operations were suspended.

The action came nearly three weeks after the Humane Society of the United States released a video showing workers at the plant using forklifts and water hoses, among other methods, to rouse cattle too weak to walk. In addition to issues of animal cruelty, the video raised questions about whether so-called downer cattle were entering the food chain in violation of federal regulations.

Although the Humane Society said at least four non-ambulatory cattle had been slaughtered for food, the USDA had repeatedly said it had no such evidence. On Sunday, federal officials said for the first time that they had evidence such cattle from Hallmark had been processed for food.

Downer cattle are not supposed to be used as meat unless a veterinarian determines that the animal stumbled or fell because of injury -- a broken leg, for instance -- that would not affect the safety of their meat. Cattle weakened by disease are not supposed to enter the food supply, although their risk of harming humans is still fairly low. There is, however, a slightly higher possibility that such cattle are suffering from bovine spongiform encephalopathy, better known as mad cow disease.

The USDA said there was only a remote possibility that the recalled beef from Hallmark could make people sick. Agriculture Secretary Ed Schafer said it was "extremely unlikely" that any cattle processed at the plant were suffering from mad cow disease.

Steve Mendell, president of Hallmark Meat Packing and its distributor, Westland, declined to comment. The company has refused to answer questions about its practices since the Humane Society video surfaced. Mendell released a statement on Feb. 3 that said he was "shocked and horrified" by the video and that the company had a long history of meeting federal safety standards.

The recall was initiated voluntarily by the company, because the federal government does not have the authority to take such action.

Some supermarkets began removing Hallmark meat from their freezer shelves immediately after the USDA's announcement.

Managers at the Costco store in Burbank said they received an urgent e-mail about 3:30 p.m. Sunday, indicating that Westland had at one time been a supplier. It was unclear whether any current stocks had been provided by the plant.

"We're going to pull it just in case," said assistant warehouse manager Roland Prydz. He said the notice involved frozen beef.

Managers at Vons and Ralphs stores in Burbank and the Silverlake-Echo Park area said they did not recognize the company and doubted that it had supplied their stores.

Because Hallmark/Westland suspended operations in early February, it is unlikely that any of its fresh meat is still being sold. "That has a very [short] shelf life and refrigerator life, so the great majority has probably been consumed," Richard Raymond, the USDA's undersecretary for food safety, told reporters.

Hallmark/Westland meat was also sold to restaurant chains, including In-N-Out Burger and Jack in the Box, but both of those companies said they stopped using it early this month after the first reports of problems at the plant.

The amount of beef affected by the recall may be far larger than 143 million pounds because meat from different companies is often mixed as it goes through numerous processors. Such mixing makes it extremely difficult for consumers to know whether meat products came from a particular plant.

At a USDA telephone briefing Sunday for retailers, school districts and food safety experts, a Costco representative raised concerns about beef that gets "commingled," according to Humane Society President Wayne Pacelle, who participated in the conference call. He said the Costco representative estimated that the amount of beef recalled may top a billion pounds.

USDA officials said the whole effect of the recall was difficult to estimate because beef from Hallmark was supplied through a "huge pipeline" that included numerous processors and distributors.

As an example, Bill Sessions of the Agricultural Marketing Service told reporters: "Coarse ground beef . . . goes into further processors, who make end items such as cooked hamburger patties, chili meat, taco meat, that type of thing, that then goes into a distributor and then is distributed to a local school system."